Pickling compound



252. COMPOSITIONS.

Qatented May 27, 1930 UNITED STATES PATENT OFFICE Examiner PERCY J. COLE CLIFFORD BANTA, OF PHILADELPHIA, PENNSYLVANIA, ASSIGNORS TO THE BARRETT COMPANY, OF NEW YORK, N. Y., A CORPORATION OF NEW JERSEY PIOKLING COMPOUND No Drawing.

metals without dissolving an appreciable quantity of the cleaned portion of the metal, and to pickling solutions for use in such processes.

One object of the present invention is to provide a pickling solution, the use of which decreases the metal loss and also the quantity of acid used during the pickling operation. Another object is to provide a solution that will not deleteriously alfect the metal, i. e. the metal upon removal from the bath Will not have turned gray or become pitted by immersion or other treatment in the pickling bath. A further object of the invention is to prevent the embrittlement of the metal which ordinarily results from the pickling operation. Embrittlement, which seriously afiects the quality of the metal, is caused by the absorption by the metal of a portion of the hydrogen evolved by the action of the acid on the metal.

In the usual treatment of iron, steel or other metals, it is necessary to remove the layer of scale and rust which usually forms thereon before the metal can be galvanized, painted or otherwise coated and treated. customarily, this is accomplished by pickling the metal in a weak solution of sulfuric or hydrochloric acid. The concentration of acid varies as much as from 2 to 15% and the temperature of the pickling bath varies over as great a range as 150 to 210 F., both variations being governed by the type of material to be pickled and by the individual production requirements. A temperature of 160 F. and the use of 5% sulfuric acid represent average pickling conditions. It is, of course, desirable to remove the rust or scale without dissolving an appreciable quantity of metal, using a minimum amount of acid, and without deleteriously affecting the metal. To accomplish this desired result, various compounds known as pickling compounds or inhibitors are added to the bath, or the bath formed containing such compounds.

In accordance with the present invention,

Application filed October 31, 1928. Serial No. 318,350.

the iron and steel or other metal is immersed, washed or otherwise treated in a picklin bath containing dilute acid, preferab y wea sulfuric acid, and an aromatic nitrile, preferably alpha naphthonitrile. We have discovered that aromatic nitriles have the property of efliciently inhibiting or minimizing the solvent action of acids, particularly inorganic acids such as sulfuric or of acid sulfates on iron, steel and other metals, and do not deleteriously affect the metals undergoing treatment. Such aromatic nitriles may in clude all compounds having the general form ula RON, in which R represents an aromatic radical. Benzo nitrile and its homologues, such as toluo or xylonitrile, or alpha naphthonitrile, beta naphthonitrile, or any mixtures of these two isomeric nitriles or other aromatic nitriles may be used.

Preferably, a naphthonitrile and more par ticularly alpha naphthonitrile is added to the pickling bath or the pickling bath formed to contain this compound. Pure alpha naphthonitrile melts at 37.5 C. and boils at 299 C. As may be determined by reference to a standard reference work on organic chemistry, aromatic nitriles can be formed by melting the alkali salts of the aromatic sulfonic acid with the corresponding alkali cyanide, and naphthonitriles can therefore be synthesized by fusing the sodium salts of naphthalene sulfonic acid with sodium cyanide to form the naphthonitrile and sodium sulfite as indicated below:

NEON NB SO;

. OsNa ON The pickling bath is preferably made by mixing .0270 by volume of the aromatic mtrile, preferably alpha naphthonitrile, with 5% sulfuric acid (by weight). The presence of the nitrile in the pickling bath results in an economy in the acid consumption; substantially prevents the dissolution of the iron, steel or other metal undergoing treatment, and embrittlement is reduced to a minimum.

The following examples will illustrate the advantages of adding aromatic nitriles to a a an.

Test pieces of soft steel measuring x x 3" were immersed for 30 minutes in 5% sulfuric acid containing naphthonitrile and in 5% sulfuric acid containing no inhibitor, both tests being conducted at 160 F. The test ieces were then removed from the pickling aths, washed, dried and weighed. The metal I losses in grams are tabulated below:

Naphthonitrile 5% acid A similar series of tests, in which the metal was immersed for 1 hours, gave the follow-' ing losses:

Naphthonitrfle 5% acid It will be noted that in every case the use of the naphthonitrile inhibitor caused a substantial saving of metal and consequently also efi'ected an economy in the acid consumption. In other words, the acid which functions to dissolve the metal when no inhibitor is used will be beneficially utilized when an inhibitor is used to dissolve rust or scale. Metal loss increases with increasing temperature of P101:-

ling. At a tem erature of 205 F., the metal loss is apprecia 1y greater than that quoted above if the specified proportion of .2 cc. of the nitrile per liter of 5% sulfuric acid is used. In this case it is desirable to double the proportion of inhibitor, thereby reducing the metal loss to a satisfactory degree.

It will, of course, be understood that numerous details of the process for pickling baths disclosed herein may be varied without departing from the. spirit of this:invention,

. and this invention is not to be limited to the nitrile.

disclosure herein but only by the scope of the appended claims.

We claim:

1. The process of pickling metals which comprises subjecting the same to an inorganic acid pickling bath and inhibiting the chemical action of the acid on the metal without interfering with the removal of scale or oxide by incorporating in the acid bath an aromatic 2. The process of pickling metals which comprises subjecting the same to a sulfuric acid pickling bath and inhibiting the chemical action of the acid on the metal without interfering with the removal of scale or oxide by incorporating in the acid bath an aromatic nitrile.

3. The process of pickling metals which the pickling solution being maintained between 150 and 210 F.

5. The process of pickling metal which comprises treating said metal with an acid reacting solution containing an aromatic nitrile, the temperature of the pickling solution being maintained between 150 and 210 F. a

6. The process which comprises treating iron or steel with an inorganic acid reacting solution containing a naphthonitrile.

7. The process of pickling iron or steel which comprises treating said iron or steel with a solution containing sulfuric acid and alpha naphthonitrile, the temperature of the pickling solution being approximately 160 F. j

8. The process of pickling iron or steel which comprises immersing said iron or steel in a bath containing approximately 5% sulfuric acid and approximately .02% by volume of alpha naphthonitrile.

9. A pickling bath for metals comprising an inorganic acid and an aromatic nitrile.

10. A pickling bath for metals com rising approximately 5% sulfuric acid an naththonitrile.

11 A pickling bath for iron or steel comprising approximately 5% sulfuric acid and alpha naphthonitrile. e

12. A pickling bath for iron or steel comprising approximately 5% sulfuric acid and approximately .02% by volume of alpha naththonitrile. I

13. A substantially non-iron dissolving solution comprising sulfuric acid and naph- I 

